1. Field of the Invention
The invention relates to a process for producing a refractory metal by chemical phase deposition of a bilayer-stacked tungsten metal, and in particular, to a process for producing a refractory metal by chemical vapor deposition of a bilayer-stacked tungsten metal through using a combination of amorphouslike tungsten nitride and a conventional tungsten metal layers to promote the reliability and stability of adjacent metal layers as well as to reduce the problem of fluorine contamination.
2. Description of the Prior Art
On view of the current technical level, in the latter stages of the manufacture of integrated circuit, it is better for the metal connector line to have a quicker propagation velocity, as well as in various process steps of the subsequent procession process, especially after heat treating, characteristics thereof shall not be caused to change. However, in the present rend, in order to search and study metal silicide having low resistance and high thermal stability, as well as to meet the requirement of ultra large integrated circuit, an device must be made from such metal silicide through a way of chemical vapor deposition. Unfortunately, typical chemical vapor deposition involves fluorine and infiltration of fluorine atom into the device will invariably impair the characteristics of the device.
In addition, according to the recent report, as the size of the device becomes smaller in the future, resistance of the interconnection line will increase in associated with the reduction of the width of the interconnection line. Therefore, it is the present trend to find a conducting material having low resistivity. While use of refractory metal silicide as the gate electrode of metal-oxide-semiconductor field effect transistor (MOSFET) or metal-oxide-semiconductor (MOS) capacitor has been studied for many years, the current topic focuses on the silicides of titanium and cobalt, whereas pure metal has been never employed due to problem of thermal stability. Further, the inward diffusion of fluorine atom during chemical vapor deposition of refractory metal and the outward diffusion of dopants from the polycrystalline silicon has been studied also.
At present, thermal stability has been considered mostly in the study and mass production of refractory metal material having low resistivity. The refractory metal silicide having lowest resistivity is titanium disilicide, but it does not exhibit sufficient thermal stability to meet the requirement of many heating steps in the subsequent procession process. Consequently, most of recent studies are directed to silicide of cobalt. However, there are problems in the silicidification of cobalt, such as, consumption of excess silicon, and lump aggregation.
In view of the foregoing, prior art materials do not how perfect designs and still have many disadvantages to be improved.
In view of various disadvantages derived from the conventional chemical vapor deposition process, the present inventors had tried to improve these and finally found, after persistently and extensively studying for many years, a process for producing a refractory metal by chemical vapor deposition of a bilayer-stacked tungsten metal, thus accomplished the present invention.